1. Field of the Invention
This invention relates to an image information signal processing apparatus, and in particular, to an image information signal processing apparatus for memorizing image information signals by means of semiconductor memories.
2. Description of the Related Art
Conventionally, an image signal memorizing apparatus has, for example, the construction shown in FIG. 1.
The apparatus shown in FIG. 1 includes input terminals 2, 4, 6, 8 and 10 for the luminance signal, the R-signal, the G-signal, the B-signal, and the composite synchronizing signal, respectively, a color/monochrome change-over switch 12, input low-pass filters (LPF) 14, 16, and 18 for preventing aliasing noise before the analog-to-digital (A/D) conversion, A/D converters 20, 22 and 24, frame memories 26, 28 and 30 for the R-, G- and B-signals respectively, a gate signal oscillator 32, a memory control circuit 34 for controlling the writing and reading of data in and out of the frame memories 26, 28 and 30, a horizontal synchronizing signal separating circuit 36, a vertical synchronizing signal separating circuit 38, digital-to-analog (D/A) converters 40, 42 and 44, output low-pass filters (LPF) 46, 48 and 50, and output terminals 52, 54, 56, 58 and 60 for the luminance, R-, G-, B- and composite synchronizing (C.SYNC) signals, respectively.
The output of the gate signal oscillator 32 provides the sampling clock signal for A/D conversion. The frequency of this sampling clock may be set, for example, to 780 f.sub.H (f.sub.H corresponds to the horizontal synchronization frequency 15.734 KHz), i.e., to 12.27 MHz. 780 f.sub.H is known as the sampling frequency resulting in a picture element length/breadth ratio of 1:1.
When using the above sampling frequency, a 5 MHz band is used for the input LPFs, 14, 16 and 18, as shown in FIGS. 2(a) to 2(c). The reason for using a 5 MHz band is that according to Nyquist's theorem, A/D conversion of a frequency equal to or more than 1/2 of the sampling frequency, i.e., 6.1 MHz, would result in aliasing noise, which would deteriorate the image quality. Accordingly, LPFs with a band of ca. 5 MHz are employed, bands of 6.1 MHz or more being cut sufficiently. LPFs with the same band, i.e., a 5 MHz band is also required by the LPFs on the output side of the D/A converters 40, 42 and 44, i.e., the LPFs 46, 48 and 50.
Recently, a so-called still video apparatus in which still image signals are recorded on a disc-like magnetic sheet with a diameter of 2 inches has come to be used. FIGS. 3 and 4 show the recording format of this still video apparatus. FIG. 3 shows the frequency allocation at the time of recording a color image signal in which the luminance signal as an FM modulation signal with a sync. tip frequency of 6 MHz and a white peak frequency of 7.5 MHz is frequency-multiplexed with the chrominance signal as a color-difference line-sequential frequency-modulated signal with center carrier frequencies of 1.2 MHz and 1.3 MHz for the R-Y and B-Y signals, respectively.
FIG. 4 shows the frequency allocation when a monochrome image signal is recorded. As shown in the figure, a format may be conceivable which enables the recording to be effected in such a manner that the luminance signal is more extended into the low frequency band because there exists no chrominance signal.
As shown in FIGS. 3 and 4, the luminance signal band for color image signal correspondence is ca. 4.5 MHz and the luminance signal band for monochrome image signal correspondence is ca. 6.5 MHz.
When freezing reproduced signals with the conventional image signal memorizing apparatus which is shown in FIG. 1 in such a still video apparatus in order to utilize them for various applications such as the attaining of special effects, the following problem is involved:
Since in the case of the above-described color image signal correspondence the band of the luminance signal (Y) is 4.5 MHz, the respective bands of the Y-signal and the color-difference signals (both R-Y and B-Y have a band of 1 MHz) when transformed into R, G and B signals will be
R.apprxeq.4.5 MHz; PA1 G.apprxeq.4.5 MHz; and PA1 B.apprxeq.4.5 MHz. PA1 image data formation means, arranged to selectively input the first image information signal or the second image information signal, for forming, when the first image information signal is input, first image data corresponding to the first image signal and second image data corresponding to the second image signal by performing sampling of the first image information signal in accordance with a first sampling signal having a first sampling frequency, and for forming, when the second image information signal is input, third image data corresponding to the third image signal by performing sampling of the second image information signal in accordance with a second sampling signal having a second sampling frequency which is higher than the first sampling frequency; PA1 first storage means capable of storing one picture plane portion of the first image data formed by the image data formation means; PA1 second storage means capable of storing one picture plane portion of the second image data formed by the image data formation means; and PA1 image data supply means for supplying, when the first image information signal is input to the image data formation means, the first image data and the second image data formed by the image data formation means to the first storage means and the second storage means, respectively, and for supplying, when the second image information signal is input to the image data formation means, the third image data formed by the image data formation means alternately to the first storage means and the second storage means, each for a predetermined period. PA1 a plurality of memory means capable of memorizing one picture plane portion of the first image data; PA1 input means for selectively inputting the first image data and the second image data; PA1 image data supply means for supplying one picture plane portion of the first image data input through the input means to one of the plurality of memory means, and for dividing one picture plane portion of the second image data input through the input means into a first sub-image data and a second sub-image data each having the same amount of information as one picture plane portion of the first image data, and supplying the first and second sub-image data to two of the plurality of memory means, respectively; and PA1 restoration means for restoring one picture plane portion of the second image data by using the first sub-image data and the second sub-image data respectively output from the two of the plurality of memory means in which the first and second sub-image data are memorized.
Accordingly, there will be no danger of the 4.5 MHz band of the above color image signals being damaged even when the band restriction to 5 MHz is effected at the input LPFs 14, 15 and 16 of the image signal memorizing apparatus shown in FIG. 1. In the case of a monochrome image signal, however, a band of 6.5 MHz is involved, as described above, so that when storing this monochrome image signal in the image signal memorizing apparatus shown in FIG. 1, it is necessary to connect the change-over switch 12 to the terminal M and to use the same input LPFs and sampling clock as in the case of a color image signal. In this case, part of the band must be cut off when freezing the signal in the image memory, so that the picture of the image of the signal read out from the image memory is deteriorated in quality.